1. Field of the Invention
The present invention relates to a touch response apparatus for an electronic musical instrument having a keyboard, which serves to detect a touch status of the key of the electronic musical instrument and to cause the touch status of the detected key to be reflected in generating the musical sound. More particularly, it relates to a touch response apparatus which generates data for a touch control of the envelope waveform of a musical sound in digital fashion.
2. Description of the Prior Art
In electronic musical instruments, it is very difficult, because of the use of switching means, to delicately transmit the touch status of a key to a sound-producing member as in a piano. Accordingly, various contrivances are made in the vicinities of keys.
In order to obtain a touch-sensitive keyboard, conventional electronic musical instruments are furnished with the touch response function of controlling the volume and tone color of a musical sound to-be-generated by detecting the depression speed or the depression pressure of a key during a key depressing operation.
Such electronic musical instrument having the touch response function generates a key depression speed detecting signal representative of the key depression speed for controlling the tone color and sound volume, besides a key-on signal.
Various arrangements have been proposed in order to produce the key depression speed detecting signal. As an arrangement for detecting the touch status of a key, there has been known one in which the period of time from the starting of the depression of the key to the end thereof is measured by a counter circuit, and the count output of the counter circuit is delivered as the key depression speed detecting signal.
This arrangement facilitates fabrication of the circuit in the form of an integrated circuit. However, it has the disadvantage of a complicated structure because the measuring counter circuits must be provided for the respective keys.
There has also been known a touch response mechanism in which each key is provided with first and second switches, these first and second switches being successively turned "on" by the depression of the corresponding key, and the difference of the times when the "on", states of the switches have been detected is found and used to determine a key depression speed.
When such touch response detection speed is used, time errors are involved in the scanning which detects the time differences of the first and second switches for all the keys, e. g., 61 keys on a keyboard. When it is intended to enhance the detecting precision, there is the problem that the keyboard scanning time must be shortened.
As a method by which the envelope waveform of a musical sound is changed depending upon the depression speed of a key, there has been one which utilizes a time constant based on a resistor R and a capacitor C. A voltage corresponding to a touch, namely, a depression speed is generated by a touch detector, and using the signal, the envelope waveform is produced by the resistor R and the capacitor C. This method is still unsatisfactory as stated below. Since all processing including, e. g., multiplication are performed in analog fashion, a processing circuit requires a large number of elements. Further, since the envelope waveforms are determined by the CR time constants, it is impossible to produce any desired envelope waveform.
In another known method, the depression speed of a key is converted into a digital value, on the basis of which an envelope value is read out from an envelope memory storing envelope values in advance, so as to produce an envelope waveform. With this method, the read-out speed of data from the envelope memory and the address position to-be-read are changed in relation to the depression speed.
The address position of the memory related to the depression speed must be accessed, and this processing is complicated.
Further, the ear of man senses the magnitude of a sound as a logarithmic function and also the variation of the sound as the logarithmic function. It is accordingly desirable that a musical sound to be generated varies as an exponential function.